Effects of fluctuation of the superconducting order parameter in a Hubbard model are investigated in the functional-integral formalism. It is shown in the framework of the Gaussian approximation that the critical temperature is drastically reduced owing to the large fluctuations of the order parameter which originate in the strong electron correlations.

• Received 25 September 1989

DOI:https://doi.org/10.1103/PhysRevB.41.1979